core: restructure IO queue callbacks

mc_resp is the proper owner of a pending IO once it's been initialized;
release it during resp_finish(). Also adds a completion callback which
runs on the submitted stack after returning to the worker thread but
before the response is transmitted.

allows re-queueing for pending IO if processing a response generates
another pending IO. also allows a further refactor to run more extstore
code on the worker thread instead of the IO threads.

uses proper conn_io_queue state to describe connections waiting for
pending IO's.

1 files changed, 3 insertions, 2 deletions

diff --git a/thread.c b/thread.c
index d3a5403..7de7d4e 100644
--- a/thread.c
+++ b/thread.c
@@ -538,10 +538,11 @@ static void thread_libevent_process(evutil_socket_t fd, short which, void *arg)
                     c->thread = me;
 #ifdef EXTSTORE
                     if (c->thread->storage) {
-                        conn_io_queue_add(c, IO_QUEUE_EXTSTORE, c->thread->storage, storage_submit_cb, storage_free_cb);
+                        conn_io_queue_add(c, IO_QUEUE_EXTSTORE, c->thread->storage,
+                            storage_submit_cb, storage_complete_cb, storage_finalize_cb);
                     }
 #endif
-                    conn_io_queue_add(c, IO_QUEUE_NONE, NULL, NULL, NULL);
+                    conn_io_queue_add(c, IO_QUEUE_NONE, NULL, NULL, NULL, NULL);
 
 #ifdef TLS
                     if (settings.ssl_enabled && c->ssl != NULL) {